Circuit interrupter



Oct. l5, 1940. M, B fWOOD 2,218,274

I CIRCUIT INTERRUPTER Filed Oct. 2, 1937 f To i@ l im Patented Oct. 15,1940 UNITED 'STATES PATENT OFFICE 2,218,214 cnwurr INTERBUPTER Morris B.Wood, Newburyport, Mass., assignor to The Chase-Shawmut Company,Newburyport, Mass., a corporation of Massachusetts Application October2, 1937, Serial No. 167,005

28Clalms.

This invention relates to circuit interrupters of the type containing afusible mass which upon fusing releases a conductor so that it is freeto move in a circuit opening direction, the fusible mass receiving heatfrom aheating element traversed by the current traversing the device.

The invention in particular relates t0 a nontamperable plug fuse type ofinterrupter andespecially one having a long center contact. lo One ofthe objects of the present invention is the provision of such a type ofinterrupter having a center contact that contains a well for the fusiblematerial, as is generally disclosed in United ,States Letters Patent No`2,168,815, l granted August 8, 1939, on an application filed in my name,and wherein the center contact member is composed of resistance materialand is so constructed and arranged as to become sufficiently highlyheated by the current traversing it to melt the fusible mass and effectthe interruption of the circuit.

For currents of relatively small value where it is somewhat diiiicult toprovide a center contact member having sufiicient resistance andmechanical strength within the available dimensions of the contactmember I prefer to make the contact member hollow and to locate withinthe contact member a resistance element which heats a fusible masslocated within the plug body to effect circuit interruption. Such aconstruction constitutes a further objectv of the invention.

Another object of the inventionl is the provision of an interruptingdevice having a center contact and means providing a receptacle for afusible mass at the upper end of the contact with an electric heatingelement within the contact and transmitting heat to the fusible masswithin the receptacle.

A furtherA object of. the invention is the pro- -vision of aninterrupter Acomprising a hollow contact member containing a heatingelement that is connected at its lower end with the contact member atvor adjacent the contact face thereof, the upper end of the heatingelement 5 passing into an insulating cup containing a fusible mass, thecup also constituting a bushing which insulates the upper end of theresistance element from engagement with the upper end of the contactmember. Another obiect of the invention is the provision of a circuitinterrupter comprising an electric resistance element .connected at oneend to a terminal of the interrupter and having at its upper end asizeable metallic mass comprised at 5g least in part of a readilyiusible metal ywhich (ci. zoo-123) normally holds a movable circuitinterrupting element in electrical connection with the upper rend of theheating element, combined with means for eiecting separation of thecircuit interrupting member and heating element upon the fusing 5 of thereadily fusible metal mass. A*

A further object of the invention is the provision of a circuitinterrupter having a fu/sible metal mass and a movable circuitinterrupting element, which can be a. fusible link, normally 10 a memberhaving tamper-preventing meansandfzo for instance, comprising an annularcylinder` concentric with the center contact and provided with teeth orother serrations at its bottom end, combined with improved means forconnecting the taglia-preventing member and body non-rotat- 25 a Anadditional object of the invention is generally to improve theconstruction and operation of circuit interrupting devices.

Fig. 1 is a plan view oi the top of a circuit 30 interrupter embodyingthe present invention.

Fig. 2 is a sectional elevation through the'interrupter.

Fig. 3 is a plan view of the top of the interrupter with the coverremoved. 35 Fig2. 4 is a section taken along line 4-4 of Fig.

Fig. 5 is a sectional detail of the interrupter taken along line 5-5 ofFig. 2.

Fig. 6 is a view similar to Fig. 2 but illustrating o the circuit opencondition of the device.

Fig. I is a detail similar to Fig. 2 but illustrating a modied form ofholder for the fusible mass.

Fig. 8 is a view similar to Fig. 7 but illustrating 5 a furthermodification.. Y

Figs. 9 and l0 are views similar to Fig. 2 but illustrating modincationswherein straight and helical Aheater elements, respectively, areassociated with fusible masses retained by the body 50 of theinterrupting device.

Fig. 11 ls a view similar to Fig. 2 but illustratingv a constructionwherein the centerv contact member constitutes both the receptacle forthe fusible mass and the heating element therefor.

but illustrating a further modiiled form 10 cuit interrupting chamber I6which is closed at the bottom by an integral bottom wall i8 and is openat the top. The top is closed by a transparent disc 20 preferably ofmica and a metal cover or cap 22, the side wall 24 of which is inturnedover the bottom edge of the enlarged head 26 of the plug body. The ca'p22 is provided with an opening or' window 28 therein which overlies theopen top of the chamber I6. The side wall of the plug body is providedwith outstanding screw threads 30 on which an exteriorly and interiorlyscrew-threaded metal terminal shell 32 is received. The bottom of theplug is provided with a recess 34 and an axially projectingannular rib36 which surrounds the recess, the terminal shell 32 having an inwardlyturned ilange 38 which is seated upon the end of the rib 36.

rl'he bottom wall I8 has a recess 40 therein formed with a flat bottomface 42 and a hexagonal peripheralwall 44, see especially Fig. 4,' inwhich is located a tamper preventing member 46 composed preferably of amolded articial resin and having an end wall 48 which is seated on thebottom face 42 of the recess and has a hexagonal periphery 50 whichengages the hexagonal periphery 44 of the recess to prevent rotation ofthe tamper preventing member in the recess. 'Said tamper preventingmember has an axially projecting cylindrical rib 5| which is co-axialwith and radially spaced inwardly from the plug o body and projectstherebelow, the end face of the rib 5i being provided with angularlyspaced series of alternate ribs 52 and recesses 54 or otherwise serratedto catch upon conductingmaterial such as tinfoil, small wires and thelike placed 45 in the recess of the socket which receives theinterrupter to disrupt the conducting material and to dislodge it frombridging relation with the terminals of the socket so as to prevent thebridging of the socket terminals by the conducting 5@ material.

A center contact member in the form of a relatively long tube 56, asshown in Fig. 2, is passed through aligned apertures in thetamper-preventing member 46 and in the bottom wall i6 55 of the plugbody i4 and has its upper or inner j/'enting member. The flanges S5 and60 iix the 70 rent rating of the device.

center contact to the plug body and maintain the tampenpreventing memberthereagainst.

nheater element comprising an electrical'resis-tance element 62 islocated within the tubular contact member coaxially therewith and hasits lower end terminated approximately flush with the lower end of thecontact member and secured electrically thereto by solder 64 or othermeans. The wire 2 is oi a diameter suited for the cur- It will berelatively small for low currents and larger for higher currents and thecomposition of the wire may be 'varied to iit the physical dimensionsand the electrical resistance thereof to the desired operatingcharacteristics of the device.

In Fig. 2 the upper end of the rod passes through a cup 66 of insulatingmaterial, such as fibre. The cup preferably has a neck 66 whichprojectsrinto the upper end of the contact tube and may be frictionallyretained therein, thereby to prevent accidental contact of the upperendy mitted lengthwise thereof into the solder withl which it is inintimate contact. The amount of solder is intended to be sulcientlygreat so that the melting thereof is delayed for a considerable periodof time following the initiation of a moderate overload current whichtraverses the heating element. The amount of the mass of solder isadjusted to secure the intended time delay of operation.

A flexible conductor 12 has the lower end thereof embedded in thefusible mass 10 and thereby normally retained' therein in electricalconnection with the upper end ofthe heater element. Said conductorextends upwardly in the chamber I6 and has a part approximatelyparallel. with the window 20 and thence passes downwardly in a channel14 of the plug body where the end thereof is electrically connected by amass of relatively high melting point solder 16 with the terminal shell32.

Spring means are provided to separate the conductor 12 and the heatingelement 62 upon the fusing of the fusible mass 10. Said spring meanscomprises a U-shaped cantilever spring generally indicated by thenumeral 16 having a pair of generally parallel legs 80 disposed onopposite sides of the conductor 12 and an integral connecting portion 62which is extended under the conductor and cross-wise thereof and bearsupwardly thereagainst. The ends 64 of the legs 80 are located invertical recesses of the plug body. The conductor maintains the spring1B normally in a depressed and tensioned position. When the metal massfuses or the conductor is ruptured the spring is released and movesupwardly into a position against the mica disc 20 as is illustrated inFig. 6, thereby insuring a rapid separation of the conductor and theheating element or a rapid separation of the ruptured ends of theconductor.

The conductor 12 for some purposes may comprise a fuse link and may havea weakened or most readily fusible portion, provided, for instance, by aperforation B6, see Fig. 5, located in that part of the link between thespring and the fusible metal mass. The link is `so constructed that itwill fuse or blow in the vicinity of the perforation only when traversedby currents of relatively high value approaching short-circuit value andwill blow practically instantly when traversed by such currents. Thearrangement of the heater element and the fusible mass, however, is suchthat the fusible mass will ultimately fuse and effect the ultimaterelease of the link and the interruption of the circuit when traversedby small overload currents. The combined arrangement thus provides for arelatively long delay of interruption on moderate overloads and aninstant interruption on short-circuit.

There are some conditions of operation where the f use link or conductor12 is traversed by a current which causes the link 'I2 to heat convsiderably, although not sufficiently to melt it.

This heat is sometimes suiiicient to anneal or remove the springiness ofthe portion 02 of the spring that underlies and is in contact with thelink. 'I'he heat, however, does not get into the legs 80 of the springand these legs retain their springiness so that the spring can functionat all times.

In the modification illustrated in Fig. 7 the solder cup 66a issupported entirely upon the end of the heating element 62 and is not inengagement with the contact tube 58. In this instance the cup 66a ismade of thin metal and is of sufficient capacity to contain enough massof solder to provide for at least the major part of the required timedelay characteristics of the device. The heater wire 62 passes looselythrough an insulating bushing 08a, which can be of glass, for instance,located in the inner end of the contact member to hold the heater wire62 from contact with the contact member. With a heater wire stiff enoughto be surely self-supporting under conditions of the device. the bushing68a can be omitted, as is illustrated in Fig. 8.

In the modification illustrated in Fig. 8 the time delay is obtainedlargely by means of a metal plate 80 which is secured to the upper endof the heating element 62 by a relatively small mass 90 of low meltingpoint solder which also serves to connect the conductor or fuse link '12with the heating element. Said plate 00 is of sufllcient mass and hassuch thermal characteristics as to delay the melting of the low meltingpoint solder 90 for the required period of time.

In the modifications illustrated in Figs. 9 and 10 the cup 66 of Fig. 2,or 68a of Fig. 7, is replaced by a cup-shaped depression or well 02formed in the inner face of the bottom wall l0 of the plug body. 'I'heupper flange 58 of the contact tube 50 is located in the bottom of thecup 92. An insulating bottom plate 94 overlies the flange and thepassage in the contact tube and is in snug engagement with thecylindrical side wall of the cupso that the low melting point solderthereabove cannot come in contact with the tube. The heating element 62is extended through the middle of the plate 04 into the cup and a lowmelting point solder mass 96 is located therein in electrical andthermal engagement with the upper end of the heating element and alsowith the lower end of the conductor 12.

In Fig. 9 the heating element is shown as a straight resistance wire. InFig'. 10 the heating element 02a is illustrated as a small diameter-wire wound in helical form so that a considerable length of wire can becontained within the contact tube. With the arrangement shown in Fig. l0the device can be made to operate upon relatively small currents, as anampere or less, although this construction can be used for largercurrents by increasing the diameter of the wire and by using wire oflower resistance.

The construction illustrated in Fig. 11 can be best used whererelatively large currents. say upwards of 10 amperes, are to becontrolled. In this construction the center contact 56a .is solid and ofitself forms the cup for the lower melting point alloy and is made ofresistance material so that it is adapted to become heated and melt thealloy to secure the operation of the device. The contact is providedwith a well 0l in its upper end` in which the low melting temperaturealloy |00 is located. The contact below the cup thereof. g A solder cupis formed in the upper endof thecontact by an insulating plug |08 orother suitable means located in the tube below the top thereof to formthe bottom wall of the cup which receives the fusible alloy H0. In thisinstance the tubular contact is made of resistance material having asidewall oi' suitable thickness to provide the desired resistance, theheat generated in the contact being transmitted into the alloy.

In the modification illustrated in Fig. 13, which in some respects ispreferred over the structure of Fig. 2, for instance, as being cheaper,the center contact ||2 is in general like the contact 06h of Fig. 12except that it is made of metal of good conductivity. A heater elementIIB, herein illustrated as a straight wire, is soldered to the innerface of the integral end `wall ||0 of the contact and carries a lowmelting alloy mass |20 at its upper end, which alloy is preferably ofconical form and cast onto the end of the wire and onto the end of thefuse link |22 in a suitably shaped mold. A tube |24 of insulatingmaterial, such as formed of a flat sheet curled into tubular iorm islocated within the center contact to insulate it from engagement withthe heater element and also to support the fusible mass, the upper endof the tube upstanding beyond the upper end of the Contact sufiicientlyto hold the mass from electrical engagement with the contact.

I claim:

1. An electric circuit interrupter comprising an insulating casing, afusible mass within said casing, a conductor within said casing normallyretained in a circuit closed position by said mass, said conductor andfusible mass being arranged for relative movement to separate saidconductor and said mass upon the fusing of said mass, and a heatingdevice for said mass carried by said casing and located mainly outsidethereof and having a part in heat transferring relation with said mass.

2. An electric: circuit nterrupter comprising an insulating casing, afusible mass within said casing, a conductor within said casing normallyretained in a circuit closed position by said mass and arranged `formovement free from said mass into a circuit open position upon thefusing of said mass, a heating device for said mass carried by saidcasing and located mainly outside'thereof and having a part in heattransferring relation with said mass, and having means externally of thecasing providing a contact face.

3. A circuit intermpter comprising a casing; a terminal structuresupported by said casing comprising means providing a well for a readilyfusible mass. 'means for heating said mass, and a contact face; and aconductor within said casing normally retained by the solidified mass ina circuit closed position, said conductor being movable to an opencircuit position upon the fusing of said mass.

4. An electric circuit interrupter comprising an insulating casing, aterminal structure on said casing having an exterior part provided witha contact face, another exterior part constituting a heat generatingelement and a part accessible from the interior of said casingconstituting a holder for a readily fusible mass, a readily fusible massin said holder, and a conductor normally retained in circuit closingposition by the solidia conducid in circuit closed position by saidsclidied mass and movable therefrom into a circuit open position uponthe fusing of said mass.

6. An electric circuit interrupter comprising a casing having an endwall, a center contact in said end wall and having its major portionextended outwardly thereof, said center contact having a well accessiblefrom the interior of the casing, a fusible mass in said Well, saidcenter contact having a least a part composed of resistance materialadapted to heat and fuse said fusible mass, and a conductor within saidcasing normally restrained in a circuit closed position by thesolidified fusible mass and arranged to move into a circuit openposition upon the fusing of said mass.

7. An electric circuit interrupter comprising a casing, a center contactof resistance material carried by and having its major portion extendingbeyond said casing, and means responsive to the heating of said contactby the current traversing it to effect interruption of the circuitthrough the interrupter.

8. An electric circuit interrupter comprising a casing, separablecircuit interrupting elements within the casing, a center contactstructure carried by and having its major portion extending beyond thecasing having at least a part composed of resistance material adapted tobecome heated by the current traversing it to effect separation of saidseparable elements and the interruption of the current.

9. An electric circuit interrupter comprising a casing, a center contactcarried by said casing having a Well accessible to the interior of thecasing and having a relatively long stem exteriorly of the casingcomposed of resistance material and terminated in a contact face, afusible mass in said well, and a circuit interrupting element normallyretained releasably in circuit closed position by the solidified fusiblemass, the electrical resistance of said contact being such as to vcausethe heating and fusing of said mass when said contact is traversed by anoverload current.

10. An electrical circuit interrupter comprising a casing, a centercontact member carried by said casing and projecting therebeyond andhaving at one end a well exposed to the interior of the casing, acontact face at the other and outer end, and an intermediate portionlocated mainly Outside of said casing and having substantial electricresistance, a fusible mass in said well, and a circuit interruptingmember normally retained releasably in circuit closed position by saidmass.

11. An electric circuit interrupter comprising a casing, a centercontact structure carried by said casing and projecting outwardlytherebeyond and comprising a member of resistance material locatedmainly outside of said casing and 5 having a well at its upper end opento the interior of the casing and a contact face at its lower end, afusible mass in said well, and a circuit interrupting element withinsaid casing normally retained releasably in circuit closed posi- 11 tionby the solidified fusible mass.

12. An electric circuit interrupter comprising a casing, a tubularcenter contact carried by and extended outwardly of said casing, meansVproviding a well within said casing, a fusible mass ll in said well, aheating element for said fusible mass located within said contact memberand connected electrically to the outer end thereof and having asubstantial part of its heating length disposed in the outwardlyextended part 21 of said tubular contact, and a circuit interruptingelement associated with the said fusible mass.

13. In an electric circuit interrupter, the combination of a casing, atubular contact member carried by said casing and extended outwardly 2.*therebeyond, a heating element within said contact member having asubstantial part of its heat generating length in that part of saidcontact member that is outwardly of the casing and having its outer endconnected electrically to the 3| outer end of said tubular contactmember and having a readily fusible mass on its other and inner end, anda circuit interrupting element associated with said fusible mass.

14. An electric circuit interrupter comprising 81 a casing having a longtubular center contact carried by and projected beyond said casing, astraight resistance element within said tubular contact and spaced fromthe inner face of the wall thereof and having its outer end only con- 41nected to the outer end of said contact, a fusible mass on the inner endof said straight resistance element, and a circuit interrupting elementassociated with said fusible mass.

15. An electric circuit interrupter comprising 4g a casing, a tubularcenter contact fixed at one end to said casing and projectedtherebeyond, a cup of insulating material located in the inner end ofsaid tubular contact, a straight resistance element extended at one endinto said cup and 5( within said contact and spaced from the inner faceof the wall of said tubular contact and fixed at its other end to theouter end of said contact,

a fusible mass in said cup, and a circuit interrupting elementassociated with said fusiblel 55 end extended through said neck intosaid cup and 55 having its outer end fixed to the outer end of saidtubular center contact, a fusible mass in said cup, and a circuitinterrupting element associated with said fusible mass.

17. An `electric circuit interrupter comprising a 70 chambered casinghaving a bottom wall, means providing a well in the bottom part of thechamber, a tubular center contact having its upper end in the bottom ofsaid weil and projected outwardly beyond said casing, a fusible mass insaid well insulated from said tubular center contact, an electricheating element within and spaced from the inner face of the wall ofsaid contact and having its inner end in electrical and thermalconnection with said fusible mass and its outer end connectedelectrically to the outer end of said center contact, and a circuitinterrupting element associated with said fusible mass.

18. An electric circuit interrupter comprising a chambered casing havingan end wall, means providing a well in the bottom part of the chamber, afusible mass in said. well, an electric heating element disposed mainlyexteriorly of said casing in electrical and thermal connection with saidfusible mass, a hollow contact member on said casing under said wellunder and insulated from said fusible mass, said contact memberenclosing said heating element and said heating element be ing insulatedfrom said contact except at one end which is connected electricallytherewith, and a circuit interrupting element associated with saidfusible mass. f

19. An electric circuitinterrupter comprising a ,casing supporting aninternally disposed fusible mass and a mainly externally disposed heatgenerating element and a circuit interrupting element which isassociated with said fusible mass and which is arranged to be separatedtherefrom upon fusing of the mass.

20. An electric circuit interrupter of the Aplug fuse typelcomprising acylindrical casing having a said center contact,-a circuit interruptingelement` associated with said fusible mass and terminal shell.

2f In an electric circuit interrupting device, a current carryingterminal composed of resistance material and constructed and arranged tobecome heated by the current traversing it, and fusible circuitinterrupting means fusible in response to the heating of said terminalto effect the interruption of the current.

22. In an electric circuit interrupting device, a fusible mass, aheating element for fusing said mass, a flexible current carryingconductor normally anchored to the solidified fusible mass, saidconductor adapted to become heated by the current traversing it, and acantilever spring for moving said conductor away from said heatingelement having a part which underlies and traverses and bears againstsaid conductor and a resilient part which is remote from the heat ofsaid conductor and exerts pressure on said trav,- erse part.

23. In an electric circuit interrupting device, an enclosing casinghaving terminals, a fusible mass within said casing connected to oneterminal, a conductor normally anchored by the solidified mass andconnected to the other terminal and adapted to become heated by thecurrent traversing it, and a cantilever spring arm having one endanchored to said casing andextended generally parallel with saidconductor and having an angularly related part extended transversely ofand underlying and exerting pressure on said conductor in a direction tomove it away from the fused mass.

24. In an electric circuit interrupter, an 'encosing casing havingterminals, a fusible mass connected to one terminal, a conductor havingone end anchored by the solidified mass and the other end connected tothe other terminal, and a U- shaped spring member for moving saidconductor away from the fused mass, said spring having the ends'of itsresilient arms anchored to said casing and its intermediate portiontraversing and underlying and bearing against said conductor.

25. An electric circuit interrupter comprising a cylindrical ceramiccasing having external screwthreads and an integral bottom wall, anexteriorly screw-threaded terminal shell screw-threaded on thescrew-threads of said casing, said bottom wall having anon-circular'recess in its outer face, a molded tamper-preventing memberhaving a non-circular peripheral portion conformed to the non-circularshape of said recess and located therein and held against independentturning thereby, a 4center contact passed through said bottom Wall andsaid tamper preventing member and clamping said wall and said membertogether, and. a circuit interrupting element in said casing connectingsaid center contact and terminal shell.

26. An electric circuit interrupter comprising a casing having achamber, a hollow center contact carried by said casing and opening intosaid chamber, a heater element having a heat generating part in saidcontact member having a readily fusible mass on its upper end withinsaid chamber, a terminal on said chamber, a conductor connected betweensaid fusible mass and terminal, and an insulating support for saidfusible mass carried by said contact member. y

27. An electric circuit interrupter comprising a casing having achamber, a hollow center contact carried by said casing and opening intosaid chamber, a heater element'having a heat generating part in saidcontact member having a readily fusible mass on its upper end withinsaid chamber, a terminal on said chamber, a conductor connected betweensaid fusible mass and terminal, and an insulating support for saidfusible mass carried by said contact member comprising an insulatingtube 'in said contact member and upstanding above the inner end intosaid chamber and disposed in engagement with said fusible mass.

28. An electric circuit interrupter comprising a casing having achamber, a hollow center contact carried by said casing and opening intosaid chamber, a heater element in said contact member having a readilyfusible mass on its upper end within said chamber, a terminal on saidchamber, a conductor connected between said fusiblemass and terminal,and an insulating support for said fusible masscarried by said contactmember comprising an insulating tube in said contact member andupstanding above the inner end into said chamber and disposed inengagement with said fusible mass, said fusible mass being of invertedconical shape seated on and partially within said tube.

MORRIS B. WOOD.

